A. c. generator-fed variable frequency motor control mechanism for an aerial lift



Sept. 6, 1966 J. M. ElTEL 3,271,645 A-C. GENERATOR-FED VARIABLE FREQUENCY MOTOR CONTROL I MECHANISM FOR AN AERIAL LIFT Filed Sept. 6, 1962 4 Sheets-Sheet 1 INVENTOR. Jay M. E i re! Attorneys Sept. 6, J. M.

A.C. GENERATOR-FED VARIABLE FREQUENCY MOTOR CON MECHANISM FOR AN AERIAL LIFT 4 Sheets-Sheet 2 Filed Sept. 6, 1962 INVENTOR. Jay M. Eire! BY w @a 26m Attorneys Sept. 6, 1966 .1 M. EITEL 3,271,645 A.C. GENERATOR-FED VARIABLE FREQUENCY'MOTOR CONTROL MECHANISM FOR AN AERIAL LIFT Filed Sept. 6, 1962 4 Sheets-Sheet 5 1 -09 I I34 3; F I g. 8 l3! INVENTOR.

g Jay M. Eifel (ZZZ fsn m Attorneys Sept. 6, 1966 J. M. EITEL 3,

A.C. GENERATOR-FED VARIABLE FREQUENCY MOTOR CONTROL MECHANISM FOR AN AERIAL LIFT Filed Sept. 6, 1962 4 Sheets-Sheet 4 I I 4 i l l w v n H m w u M w a m m z u 4 A IIIIJ. 4 m W M a II I ||l|l|l| II D O A I W 1:11.; p 91 J) m u a 9 w n1. R U 3 Z w 1 Z M r. z m g N 0 02 1 Z M .l .w I I N a R a a F m E; I ll Illll'llllollvl m I H N T Q N II- 1| w vM 4 0 (HF W mg w W E A 2 Z m 3 A m 0 W 5 c w m WW O I L ..N.\ 5: t 0\ m 1/, 117 G n 1 Q 0 m P I- fl m q H AJ- MM M M w n a n "17? 1 6-21! (MA I Fig. IO

INVENTOR. Jay M. Eire! Attorneys United States Patent Ce 3,271,645 A.C. GENERATOR-FED VARIABLE FREQUENCY MOTQR CONTROL MECHANISM FOR AN AERIAL LIFT Jay M. Eitel, Los Altos, Calif, assignor to Telsta Corp.,

San Carlos, Calif, a corporation of California Filed Sept. 6, 1962, Ser. No. 221,693 11 Claims. (Cl. 318-148) This invention relates to a control mechanism and system, and more particularly to a control mechanism and system for controlling the movement of a boom structure.

In the operation of aerial lifts in which a boom structure having a workmans basket pivotally mounted on its outer end, it is often desirable to have available more than one rate of speed for moving the boom structure. For example, in the initial raising or moving of the boom structure from its at-home position into a general location in which it is desired to perform work, it is often desirable to accomplish this portion of the movement of the boom structure very rapidly because precise movement at this stage is not required. However, as the workmans basket or platform approaches the general Work area, it is generally desirable to slow down the movement and to approach the work area at a slower speed. Then, for very precise positioning of the workmans basket, it is often desirable to be able to move the boom structure and the workmans basket connected thereto at a relatively slow speed so that the workmans basket can be precisely positioned without danger of damaging the structure on which work is to be performed or of damaging the workmans basket or the boom structure. Such precise control may be particularly desirable when working in proximity to high voltage power lines, etc. At the present time, such equipment is not available.

In general, it is an object of the present invention to provide a control mechanism and system in which it is possible to change the speed of movement of the boom structure.

Another object of the invention is to provide a control mechanism and system of the above character which can be utilized for increasing or decreasing the speed of movement of the boom structure.

Another object of the invention is to provide a control mechanism and system of the above character in which the operator in the workmans platform can change the speed of movement of the boom structure.

Another object of the invention is to provide a control mechanism and system of the above character which can be incorporated with relatively minor changes in conventional aerial lifts.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment is set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE 1 is a side elevational view of an aerial lift incorporating my control mechanism and system.

FIGURE 2 is a diagram illustrating a control mechanism and system incorporating my invention.

FIGURE 3 is a side elevational view in cross-section of a control mechanism incorporating my invention.

FIGURE 4 is a cross-sectional view taken along line 4-4 of FIGURE 3.

FIGURE 5 is a partial cross-sectional view on the side opposite the side shown in FIGURE 3.

FIGURE 6 is an enlarged detail view of a portion of the system as shown in FIGURE 2.

FIGURE 7 is a still further enlarged detail view of a portion of the system shown in FIGURE 6.

FIGURE 8 is an enlarged cross-sectional view taken along line 88 of FIGURE 7.

3,271,645 Patented Sept. 6, 1966 FIGURE 9 is a circuit diagram of my system.

FIGURE 10 is a circuit diagram of a modification of my system.

In general, my system for controlling the movement of a boom structure in an aerial lift consists of a power supply and motor drive means for moving the boom structure. Control means is provided for connecting the motor drive means to the power supply. The control means includes means for changing at least one of the characteristics of the output of the power supply so that said output characteristic has at least two values. The output characteristic is one which, when its value is changed, the speed of operation of the motor drive means is changed.

My control mechanism and system for controlling the movement of a boom structure can be incorporated in any suitable aerial lift. For example, as shown in FIG- URE 1 of the drawings, it can be incorporated in a mobile aerial lift 11 which consists of a self-propelled vehicle 12 having front and rear wheels 13 and 14. A framework 16 is supported by the front and rear wheels. A cab 17 of conventional construction is mounted on the front portion of the framework 16.

A lifting equipment 18 is mounted on the rear portion of the framework 16 and includes a lift supporting structure or turret 19 which is rotatably mounted upon a vertical support post 21 carried by the frame 16. Motor drive means 22 is provided for rotating the lift supporting structure 21 about the vertical axis formed by the post 21.

An extensible boom structure 23 is pivotally mounted at 24 in the lift supporting structure 19 for swinging movementor raising and lowering of the outer end of the boom structure 23 about the horizontal axis provided by the pivot 24. Motor operated means 26 is mounted within the lift supporting structure 19 and is provided for swinging the boom structure 23 about the horizontal axis.

The boom structure 23 consists of an outer boom 27 and an inner boom 28 which telescopes within the outer boom. Motor drive means 29 is provided for extending and retracting the inner boom 28 with respect to the outer boom 27. A workmans basket 31 is pivotally mounted on the outer end of the inner boom section 28 and carries a control mechanism 32 for controlling the movement of the boom structure 23 as hereinafter described.

The aerial lift also includes a motor generator set 36 which is mounted within the lift supporting structure 19 and a control panel 37 which is also mounted within the lift supporting structure 19. In addition to the control mechanism 32 which is provided on the workmans basket, there is a control mechanism 38 which is removably secured to the exterior of the lift supporting structure 19 and which has a long control cable. The control mechanism 38 can be used for ground control or control from the vehicle itself when the vehicle is moving to control the boom structure.

A cable guiding and cable carrying apparatus 41 is mounted on the vehicle intermediate the ends of the same and is of the type described in my copending application Serial No. 93,684, filed March 6, 1961, now Pat. No. 3,226,087. Additional cable guiding means 42 is mounted on the boom structure and also is of the type described in my copending application Serial No. 93,684, filed March 6, 1961.

All portions of the aerial lift 11 thus far described are disclosed in issued patents and copending applications. Reference may be made to my Patents 2,841,404; 2,896,- 750; 2,936,847; and application Serial No. 560,621, filed January 23, 1956, now Pat. No. 3,055,459.

The control mechanism 32 which forms a part of my system for controlling movement of the boom structure will first be described. Portions of the control mechanism are similar to the control mechanism for electrically driven apparatus disclosed in Patent No. 2,627,560 and in the control mechanism described in Patent No. 2,841,- 659. The control mechanism consists of an upper housing 51 formed of a suitable material such as an aluminum casting. A control lever 52 extends upwardly through a centrally disposed opening 53 provided in the upper portion of the housing 51. The control lever 52 consists of an outer tubular member 54 which is formed in two parts, an upper part 54a and a lower part 5412. The two parts 54a and 54b are maintained in alignment and the upper part 54a is rotatable with respect to the part 541) for a purpose hereinafter described. The lower part 5412 is slidably mounted in a tubular member 56 and is provided with a horizontally extending pin 57 which extends through a slot 58 provided in the tubular member 56 to limit the relative longitudinal movement between the tubular member 54 and the tubular member 56. The lower end of the tubular member 56 is secured to one end of a universal joint 59 by suitable means such as a screw 61. The universal joint is secured to a base plate 62 by suitable means such as a cap screw 63. The base plate 62 and a lower housing 64 are secured to the upper housing 51 by suitable means such as cap screws (not shown). Sealing gaskets 66 are provided between the base plate 62 and the upper housing 51 and the lower hon-sing 64.

A plurality of microswitches, namely four, identified as CS3A, CS-4A, CS-SA and CS-6A, are disposed in a horizontal plane within the upper housing 51 and are secured to the base plate 62 by suitable means such as brackets 67. The microswitches CS3A through CS6A are provided with operating levers 68 which are adapted to be engaged and operated by a horizontally extending flange 69 carried by the lower portion of the tubular member 56 as the control lever 52 is swivelled or pivoted in much the same manner as a joy stick.

A mounting block 71 is formed as a part of the tubular member 56 and carries a pair of microswitches CS-IA and CS-2A which have operating arms 72 adapted to be engage-d by operating levers 73. These operating levers 73 are adapted to be engaged by the pin 57 as the tubular member 54 is raised and lowered as described in my Patent No. 2,841,659 to operate the switches (IS-1A and CS2A.

The control lever 52 also includes a central rod 76 which is slidably mounted in the tubular member 54 for movement longitudinally of the tubular member. The lower extremity of the rod 76 is adapted to engage a leaf spring member 77 which extends into an elongate vertical slot 7 8 provided in the lower part 5417 of the tubular member 54. This spring member is mounted on a block 79. A microswitch CS7A is also mounted upon the block 79 and is provided with an operating lever 81 which is engaged by the spring member 77 and which is adapted to be operated by vertical movement of the rod 76 and the spring member 77.

Means is provided for yieldably retaining the control lever 52 in a vertical position within the housing 51 and consists of a coil spring 83 which has its lower end seated within the upper extremity of the upper housing 51 and which has its upper'and smaller end secured to the control lever 52. The upper end of the control lever 52 is provided with an outer cylindrical covering 84 which is mounted over the tubular member 54. The upper end of the coil spring 83 is secured to the lower extremity of this cover 84 by a nut 86 which is threaded onto the lower end of the covering 84 and retained thereon by a set screw 87. A collar 88 is also threaded onto the lower extremity of the covering 84 and serves to provide a space between it and the nut 86 which retains the upper end of the spring 83. A protective conical corrugated spring-like covering 89 formed of a suitable material such as rubber or Neoprene has its upper extremity frictionally engaging the covering 84 and has its lower extremity secured to the upper portion of the upper housing 51 by a retaining ring 91 and screws 92.

A control knob 93 also forms a part of the control lever 52 and is secured to the upper part 54 of the tubular member 54 by suitable means such as a set screw 94. A horizontal pressure plate 96 is mounted within the knob 93 and is adapted to engage the upper extremity of the control rod '7 6 so that it can be depressed against the force of a spring 97 disposed over the end of the control rod 76. A disc 98 of suitable material such as neoprene overlies the pressure plate 96 and is held in place by a plate 99 which overlies the disc 98 and a cap 101 which is threaded onto the knob 93.

This part of the construction of my control mechanism, with the exception of formation of the tubular member 54 in two separate parts 54a and 54b, is very similar to the construction disclosed in my Patent No. 2,841,659.

At least one and preferably two or more additional microswitches are incorporated in my new and improved control mechanism. In the embodiment shown in the drawing, two additional microswitches identified as CS- 8A and CS-9A have been added. These microswitches CS-SA and CS-9A are supported upon brackets 106 mounted'upon the horizontally extending flange 107 provided on the upper end of the tubular member 56 as shown particularly in FIGURE 3. These microswitches are provided with levers 108. Means is provided for operating levers 108 and also for providing a slip joint for the upper and lower parts 54a and 54b of the tubular member 54 and consists of a pair of members 109 which are provided with a pair of vertical spaced semicircular flanges 111 which are slidably seated in horizontal grooves 112 provided in the lower end of the upper part 54a and the upper end of the part 54b. Suitable means is provided for securing the two members 109 about the tubular member 54 and consists of bolts 113.

Each of the members 109 is provided with an enlarged portion 109a which is adapted to engage the operating lever 108 of the associated microswitch as shown particularly in FIGURE 4. Means is provided for retaining the tubular member 54 and the control rod in a neutral position with respect to microswitches CS-8A and CS-9A and consists of compression springs 116 mounted between portions 10% of the members 109 and brackets 117 secured to the flange 107 of the member 56.

Operation of this control mechanism will be described in conjunction with my system.. My system, in addition to the control mechanism 32, includes a pair of solenoids 80-1 and SO-2 which are mounted upon the motor 36A of the motor generator set 36. They are utilized for controlling the output frequency of the generator 36B as hereinafter described. The motor generator set forms the power unit for the motive drive means 22, 26 and 29.

Although I have shown electrically operated motor drive means for my lift, it is readily apparent that, if desired, hydraulic control means can be provided. In this event, hydraulic motors can be utilized for the motor drive means 22, 26 and 29 and a motor driving a hydraulic pump supplying hydraulic fluid to the hydraulic motors can be utilized for the power supply. The solenoids -1 and SO'2 could then be utilized for'controlling the pressure at which fluid is supplied to the hydraulic motors and thus vary the speed of rotation of the hydraulic motors. The pressure supplied to the hydraulic motors can be readily controlled by changing the pres sure at which the fluid is returned to the reservoir for the hydraulic fluid.

Assuming that electrically operated motive drive means is utilized, the motor generator set can be of any suitable type. For example, it can be Model No. 305 CCK-SR manufactured by D. W. Onan & Sons, Inc. of Minneapolis, Minn., which is a 3.5 kw. generator that supplies 3 phase 60 cycle 230 volt A.-C. at 1800 rpm. The generator is provided with a saturated field which has inherent voltage regulation. Alternatively, the motor generator set can be Model No. SRMSI manufactured by Kohler which has a similar output but which is provided with a con-. trollable field.

Assuming that an Onan type motor generator set is utilized as shown in the drawings, the solenoids 50-1 and 80-2 are mounted on the motor 36A so that they can control the operation of the governor for the motor. As is well known to those skilled in the art, such a motor generator set is provided with a fuel pump 121 which supplies fuel to a carburetor 122 through a fuel line 123. The carburetor is provided with a throttle plate 124 for controlling fuel flow. This throttle plate is secured to a throttle arm 126. The throttle arm is pivotally connected to a link 127. This link 127 is pivotally connected to an arm 128 which has its other end secured to a governor control rod 129. The governor control rod 129 is provided with a substantially U-shaped yoke 131 which engages opposite sides of a center pin 132 of the governor. A snap ring 133 is provided on the center pin 132 for retaining the yoke 131 in engagement with the pin. The center pin 132 is retained in a cam shaft 134 which rotates as the motor operates. A cam shaft gear 136 is affixed on the cam shaft 134 and rotates with the cam shaft. It is provided with a race 137 in which are disposed a plurality of governor fly balls 138. A governor cup 139 is mounted on the center pin 132 so that the center pin can rotate with respect to the governor cup. As can be seen from FIGURE 8, the outer extremities of the governor cup are tapered inwardly toward the cam shaft gear so that as the speed of the cam shaft gear is increased, the governor fly balls will be thrown centrifugally in a radial direction to urge the governor cup 139 outwardly to move the linkage 127 to the right as viewed in FIGURES 7 and 8 to change the positioning of the throttle valve 124 and to decrease the fuel supplied to the carburetor 122. It will be noted that the force of the governor fiy balls must overcome the effect of a spring 141 which has one end secured to an adjustable mounting bracket 142 and the other end secured to a pin 143 which is aflixed to the fuel pump 121.

The governor on this motor operates in a conventional manner to drive the generator at a relatively constant speed as, for example, the 1800 r.p.m. specified. The positioning of the spring 141 on the bracket 142 determines the sensitivity of the governor and the speed of the governor is controlled by adjusting the nut 144 provided on the pin 143. Increasing the tension on the spring 141 increases the force which the governor must overcome and, therefore, increases the speed at which the motor 36A must operate before the governor throttles the speed. Similarly, decreasing the tension on the spring 141 decreases the speed at which the governor will throttle the operation of the motor.

The solenoids SO1 and 80-2 are provided with means whereby they can affect the operation of the governor and thereby control the speed of the motor. Thus, the solenoids 80-1 and 50-2 have been mounted in brackets 146 which are mounted on the motor 36A on opposite sides of the arm 128 of the governor control linkage. The solenoid SO-1 is provided with an operating arm 147. A spring 148 has one end attached to the operating arm 147 and has the other end secured to the bracket 142 of the arm 128. Similarly, the solenoid 80-2 is provided with an arm 151. A spring 152 has one end secured to the arm 151 and has the other end secured to the bracket 142 at substantially the same point as the spring 148. When either of the solenoids SO1 and SO2 are energized, the springs 148 and 152 counter-balance each other and thus have no effect on the normal operation of the governor. However, when one of the solenoids is energized, it will affect the operation of the governor. For example, when SO-1 is energized, the spring 148 will be tension to a greater extent to aid the spring 141 so that the governor must exert additional force to overcome the additional force created by the spring 148 before it can throttle the motor 36A. This means that the motor will be operating at a higher governed speed. When the solenoid 50-2 is energized, and the solenoid 80-1 is in a deenergized condition, the additional tensioning of the spring 152 will create a force opposite to that created by the spring 141 so that less force must be exerted by the governor before it can throttle the motor 36A. This means that the motor 36A will operate at a lower governed speed than would be the case when solenoid SO2 is not energized.

A simplified version of the circuitry utilized in my system for controlling the boom structure 23 is shown in FIGURE 9. The microswitches provided in the control mechanism 32 are indicated on the circuit diagram. The corresponding microswitches in the control station 38, with the exception of the microswitch CS7A which is omitted from the ground control station 38, are indicated as CS1 through CS-9. The relays associated with these switches are indicated as RY1 through RY9. No relay is associated with the microswitch CS-7A. The relays are provided with the contacts shown which are connected to the three phase lines from the generator 368 and which are adapted to drive the associated motor as indicated in the circuit diagram. These relays which also may be called contactors are adapted to be energized from a single phase transformer which is connected across two of the lines from the generator 36B to supply a low voltage, e.g., 12 volts, to the relays. A separate battery 156 is provided for energizing the relays associated with the motor generator set.

Operation of my control mechanism and system for controlling the movement of the boom structure 23 may now be briefly described as follows. Let it be assumed that the boom structure is mounted in a position in which it extends over the cab of the vehicle and that it is now desired to utilize the same. The ground control station 38 can be removed from the lift supporting structure or turret 19 to move the boom structure to a position so that the basket is close to the ground so that an operator can step into the basket. If it is desired to accomplish this and with the normal speed of operation of the generator 36, the desired switches of the switches CS-l through CS6 are operated. For example, if it is desired to raise the boom structure, the switch CS3 is operated. Thereafter, when the boom structure has been raised sufliciently, the switch can be released and the boom structure can be rotated in a clockwise or counter-clockwise direction by operating either the switch CS-S or CS-6 to move the boom structure out to the side of the vehicle. Thereafter, the boom structure can be lowered by operation of the switch CS4.

If it is desired during these operations to move the boom structure more rapidly, the switch CS8 can be moved to a closed position during the same time. Closing of this switch will energize the relay RY-8 to close its contacts to energize the solenoid SO-l. Energization of the solenoid SO1 tensions the spring 148 to aid the spring 141 and to, therefore, make it necessary for the motor 36A to increase the governor speed before the governor can throttle the engine. Increasing the speed of the motor 36A will increase the output frequency of the generator 36B as well as the output voltage. In increasing the speed of the motor, it is desirable to change at least one of the characteristics of the output from the generator. It is desirable that the characteristic which is changed be one which will also change the speed of rotation of the drive motors which are being operated to move the boom structure. Thus, for example, the rod 147 connected to the solenoid SO-l can be adjusted so that the spring 1148 applies suflicient force so that the motor will operate at a speed which will cause the generator to produce an output frequency of 75 cycles rather than the normal 60 cycles. This will cause the drive motor being utilized for operating the lift to be rotated at a substantially faster speed and thereby increase the speed of movement of the boom structure.

If it is desired to move the boom structure more slowly than the normal speed, the switch CS9 can be operated 7 to energize the relay RY-9 and the solenoid 80-2. Energization of the solenoid SO2 tensions the spring 152 to reduce the force applied by the spring 141 so that the motor 36A of the motor generator set will be controlled sooner and at a lower speed by the governor. This will decrease the frequency output of the generator as well as reduce the voltage. This reduction of the frequency of the generator will reduce the speed of rotation of the drive motor which is being operated.

Thus, it can be seen that the operation of these switches in the ground control station 38, the boom structure may be moved at its normal speed by operating the generator at 60 cycles, a faster speed by operating the generator so that it produces 75 cycles, or at a lower speed by operating the generator so that it produces a frequency of 45 cycles.

Now let it be assumed that the boom structure has been positioned so that the workman can readily enter the workmans basket 31. Thereafter, the workman in the workmans basket can assume control of the operation of the boom structure by utilizing the control mechanism 32. He can operate the drive motors 22, 26 and 29 at their normal speeds by grasping the control lever 52 by the hand and utilizing the thumb to depress the pressure plate 96 to operate the rod 76 which closes the microswitch CS7A. After this has been accomplished, any of the desired microswitches in the control mechanism may be operated. For example, if it is desired to raise the boom structure, the control lever 52 is lifted so that the tubular member 54 and the pin 57 connected thereto is lifted to operate the microswitch CS3A. Operation of switch CS3A causes energization of the relay RY-3 and closing of the contacts associated therewith to operate the lift motor to raise the outer end of the boom structure. Conversely, the boom structure can be lowered by moving the control lever downwardly so that the pin 57 operates the microswitch CS4A.

The boom structure can be extended or retracted by operation of the microswitches CSlA and CSZA. The switches are operated by moving the control lever 52 forwardly or rearwardly to shift the cam plate 69 to operate the operating levers 68 of the microswitches. The boom structure can be rotated by operation of the control lever 52 to one side or the other. For example, it can be moved in a clockwise direction by shifting the control lever to the right to operate the microswitch CS-SA. Conversely, the boom structure can be moved in a counter-clockwise direction by operation of the microswitch CS6A by moving the control lever to the left as viewed in FIGURE 3.

If it is desired to move the boom structure more rapidly in the direction in which it is being moved, it is only necessary to rotate the control lever 52 in a clockwise direction to energize the microswitch CS8A which energizes the relay RY-8 which, in turn, energizes the solenoid 80-1 to cause the motor to operate at a faster speed so that the generator will supply an output having a higher frequency. As explained above, this causes the drive motor being operated to operate at a greater speed.

After the boom structure has been initially moved rapidly to the general location desired, the control lever can be allowed to return to its normal position under the urging of the springs 116 and the boom structure can thus be allowed to approach the desired position at its normal speed. Thereafter, if it is desired to precisely position the boom structure after it has once arrived at the general location, it may be desirable to operate the boom structure at a lower rate of speed. This can be accomplished by rotating the control lever in a counter-clockwise direction to cause the operation of switch CS9A which causes energization of the relay RY-9 and the solenoid SO-Z so that the motor will be operated at a lower speed and decrease the output frequency from the generator 36B. This will cause the drive motors being utilized for driving the boom structure to be operated at a slower speed and will make it possible to precisely position the boom structure Without danger of accidentally moving the boom structure into undesired locations or in damaging the boom sructure of the workmans basket.

A more simplified embodiment ofmy system for controlling the boom structure 23 is shown in FIGURE 10. In this embodiment, a control mechanism of the type described in my Patent No. 2,841,659 can be utilized. One of the solenoids SO1 or SO2, with its associated spring, can be omitted depending upon whether an increased speed or a decreased speed is desired. Let it be assumed that an increased speed is desired. If such is the case, solenoid SO2 and its associated spring 152 can be omitted.

Relay RY8 is provided for energizing the solenoid SO1. The relay RY8 is connected to an extra set of contacts which is provided for each of the relays RY-l through RY6 as shown in FIGURE 10. Thus, when any one of the switches CSl through CS6 and CS-lA through CS6A is closed, the associated relay will be operated to cose its contacts to energize the associated drive motor for the boom structure. At the same time, as soon as one of the relays RY-l through RY-6 is energized, the relay RY8 will be energized to close its contacts to energize the solenoid SO1. Energization of the solenoid SO-l will tension the spring 148 to apply additional force to the arm 28 which aids the spring 141 so that the motor 36A must operate at a faster speed before the governor controls the speed of the motor.

It, therefore, can be seen that with this arrangement, each time one of the drive motors 22, 26 and 29 is energized, the soilenoid SO1 will be energized so that the generator 36 will increase its output frequency to thereby increase the speed of movement of the boom structure. If desired, the solenoid SO2 can be operated instead of the solenoid SO1 to provide an arrangement in which the boom structure will be operated at a slower speed.

In both of the circuit diagrams shown in FIGURES 9 and 10, there will be a relatively smooth transition from one speed of movement to the other because the output frequency from the generator will not be increased instantaneously but rather will be increased or decreased gradually as the motor 36A increases or decreases its speed. Therefore, there Will not be any abrupt or jerky movements of the boom structure which makes it possible to control the movement of the boom structure very precisely with the desired amount of speed and accuracy.

It is apparent from the foregoing that I have provided a new and improved control mechanism and system which is particularly adapted for controlling the movement of boom structures. Although I have limited my description to controlling the movement of boom structures, it is readily apparent that this same control mechanism and system can be utilized for controlling other types of apparatus if desired. Also, as pointed out above, although I have generally limited my description primarily to electrically driven drive means, it is readily apparent that the same teaching can be applied to other types of drives as, for example, hydraulic means as explained above.

I claim:

1. In a system for controlling the movement of a boom structure in an aerial lift, first A.-C. motor drive means for rotating the boom structure about a vertical axis, second A.-C. motor drive means for raising and lowering the outer end of the boom structure about a horizontal axis, and third A.-C. drive means for moving the outer end of the boom structure to and fro, a motor generator set having an AC. electrical output, and manually operated control means for connecting the electrical output of the motor generator set to the first, second and third drive motors so that the first, second and third drive motors can be selectively energized, said manually operated control means also including means for changing the speed of operation of the motor generator set to change the frequency of the electrical output so that the selected drive motor or motors will be operated at a different speed.

2. A system as in claim 1 wherein said means for changing the output frequency of the generator is operated each time the control means is operated.

3. A system as in claim 1 wherein said means for changing the output frequency of the generator can be selectively operated.

4. A system as in claim 1 wherein the manually perated control means includes a control mechanism consisting of a housing, a control lever mounted in the housing for movement therein, switch means mounted on the control lever, a portion of the control lever being rotatable, and means carried by the rotatable portion of the control lever for operating the switch means in any position of the control lever.

5. A system as in claim 1 wherein said motor generator set includes governor means for regulating the speed of the motor generator set, and wherein the manually operated control means includes solenoid means, and means controlled by the solenoid means for adjusting the governor so that the motor generator set operates at a different speed.

6. A system as in claim 5 wherein the governor means includes a governor and a governor linkage, the governor linkage being adjustable to determine the normal governed speed of the motor, and wherein the means controlled by the solenoid means includes means engaging the governor linkage for changing the governed speed of the motor generator set.

7. A system as in claim 6 wherein the solenoid means includes a pair of solenoids each having an actuator, springs connecting the actuators of each of the solenoids to the governor linkage, one of the solenoids being positioned that when it is energized, it causes the speed of the motor generator set to be governed at a speed which is less than the normal governed speed and wherein the other solenoid is positioned so that when it is energized, it causes the speed of the motor generator set to be governed at a speed which is less than the normal governed speed.

8. In apparatus of the character described, a mobile self-propelled vehicle, a lifting equipment mounted upon the vehicle, said lifting equipment including a boom structure, a Workmans platform mounted on the outer end of the boom structure, motor drive means including a plurality of motors forming a part of the lifting equipment and serving to cause rotation of the outer end of the boom structure about a vertical axis, raising and lowering the outer end of the boom structure about a horizontal axis and movement toward and away from the vehicle, a motor generator set mounted on the vehicle, said motor generator set comprising an internal combustion engine serving as a motor and a generator driven by the engine, said generator having an electrical output, means connecting the electrical output of the generator to the plurality of motors of the motor drive means for the lifting equipment, said last named means including a manually operated control mechanism for obtaining a plurality of speeds of operation of said motors, and means controlled by the control mechanism for changing the speeds of operation of the internal combustion engine to thereby change the frequency of the output from the generator and to thereby change the speed of rotation of the plurality of motors of the motor drive means for the lifting equipment.

9. In a system for controlling the movement of a boom structure and an aerial lift, a motor generator set having an electrical output, motor drive means for moving the boom structure, and control means connecting the motor drive means to the electrical output of the motor generator set to energize the motor drive means, said control means including manually controlled means for causing said motor generator set to operate at speeds so that its electrical output will have frequencies above and below a normal frequency to thereby cause said motor drive means to operate at speeds less than and greater than the normal speed and to thereby increase or decrease the speed of movement of the boom structure relative to the normal speed, said motor drive means including first, second and third drive motors, the first of the drive motors being utilized for rotating the boom structure about a vertical axis, the second of the drive motors being utilized for raising and lowering the outer end of the boom structure about a horizontal axis, and the third of the drive motors being utilized for extending and retracting the boom structure, said manually controlled means including means for selectively operating said first, second, and third drive motors.

10. In an apparatus of the character described, a mobile self-propelled vehicle, a lifting equipment mounted upon the vehicle, said lifting equipment including a boom structure, a workmans platform mounted on the end of the boom structure, motor drive means forming a part of the lifting equipment and serving to ause rotation of the outer end of the boom structure about a vertical axis, raising and lowering of the outer end of the boom structure about a horizontal axis and movement toward and away from the vehicle, a motor generator set mounted on the vehicle, said motor generator set comprising an internal combustion engine serving as a motor and a generator driven by the engine, said generator having an electrical output, means connecting the electrical output of the generator to the motor drive means for the lifting equipment, said last named means including a manually operated control mechanism, and means controlled by the control mechanism for changing the speeds of operation of the internal combustion engine to thereby change the frequency of the output from the generator and to thereby change the speed of rotation of the motor drive means for the lifting equipment, said internal combustion engine including a speed control governor mounted thereon and being set so that the internal combustion engine is normally driven at a predetermined speed, said means controlled by the control mechanism including means for adjusting the governor so that the internal combustion engine operates at speeds different from the normal speed.

11. Apparatus as in claim 10 wherein said control mechanism consists of a housing, .a control lever mounted on the housing for movement therein, said control lever comprising first and second parts, switch means mounted on one of said parts, the other of said parts being rotatable with respect to said one part, means carried by the rotatable part for operating the switch means in any position of the control lever, and means controlled by the switch means for adjusting said governor.

References Cited by the Examiner UNITED STATES PATENTS 910,638 1/1909 Bradley 318-147 1,855,892 4/1932 Schiebler 3l939 X 2,213,089 8/1940 Deep et a1 318157 2,567,883 9/1951 Gray 318-154 X 2,627,560 2/ 1953 Eitel 2005 2,841,659 7/ 1958 Eitel 200-5 3,099,779 7/ 1963 Hallsworth 318157 FOREIGN PATENTS 1,143,661 10/ 1957 France. 1,159,232 6/ 1958 France.

851,225 10/1952 Germany.

ORIS L. RADER, Primary Examiner. T. LYNCH, Assistant Examiner. 

1. IN A SYSTEM FOR CONTROLLING THE MOVEMENT OF A BOOM STRUCTURE IN AN AERIAL LIFT, FIRST A.-C. MOTOR DRIVE MEANS FOR ROTATING THE BOOM STRUCTURE ABOUT A VERTICAL AXIS, SECOND A.-C. MOTOR DRIVE MEANS FOR RAISING AND LOWERING THE OUTER END OF THE BOOM STRUCTURE ABOUT A HORIZONTAL AXIS, AND THIRD A.-C. DRIVE MEANS FOR MOVING THE OUTER END OF THE BOOM STRUCTURE TO AND FRO, A MOTOR GENERATOR SET HAVING AN A.-C. ELECTRICAL OUTPUT, AND MANUALLY OPERATED CONTROL MEANS FOR CONNECTING THE ELECTRICAL OUTPUT OF THE MOTOR GENERATOR SET TO THE FIRST, SECOND AND THIRD DRIVE MOTORS SO THAT THE FIRST, SECOND AND THIRD DRIVE MOTORS CAN BE SELECTIVELY ENERGIZED, SAID MANUALLY OPERATED CONTROL MEANS ALSO INCLUDING MEANS FOR CHANGING THE SPEED OF OPERATION OF THE MOTOR GENERATOR SET TO CHANGE THE FREQUENCY OF THE ELECTRICAL OUTPUT SO THAT THE SELECTED DRIVE MOTOR OR MOTORS WILL BE OPERATED AT A DIFFERENT SPEED. 